There are many applications where it is desirable to initiate a chemical reaction on a sample. Commonly the samples are located on a microscope slide. Typical reactions include immuno-histochemical reactions of cellular material, or in situ-hybridisation of DNA or RNA. In other forms, microarrays of thousands of small samples of material, including DNA, RNA proteins or small chemical compounds are attached to a microscope slide, where it is desirable to promote a chemical reaction between the material on the slide and other chemicals or fluids. These reactions require controlled conditions, including controlled reaction time, temperature and concentration of chemicals. It is important that the reaction across the slide is uniform, and also that reactions from slide to slide are consistent.
It is also important to minimise evaporation and overall fluid quantity used.
In the past, chemical reactions taking place on slides have been controlled by skilled persons adding and mixing the reagents. This allowed the time and quantity of the reagents to be controlled for each slide. However, this procedure is time consuming, required highly skilled operators, and can produce inconsistent results from slide to slide.